The Xi’an City Wall, located in Shaanxi Province, is one of China’s best-preserved ancient city walls and a world-renowned historical landmark.
Riebo conducted a full-scale drone-based oblique photogrammetry survey to digitize and preserve this 13.74 km structure in 3D — providing an accurate and detailed digital twin for future restoration and management.
Project Background
With increasing emphasis on cultural heritage digitization, the project aimed to achieve high-precision 3D reconstruction while minimizing environmental disturbance.
Using UAV-based close-range imaging, the team captured fine surface details and architectural features of city gates, towers, and ramparts — essential for historical documentation and digital preservation.
Survey Area and Data Collection
- Survey scope: Entire 13.74 km perimeter of Xi’an City Wall and surrounding ancient structures (≈ 14 km² area).
- GCP setup: 48 ground control points using non-invasive, identifiable surface markers.
- Flight timing: 9:30 – 16:00 to ensure balanced light and minimal shadow interference.
- Resolution:
- Orbit flight at 150 m — 2 cm GSD
- Close-range flight at 45 m — 4 mm GSD
A total of 2,325 photographs were collected for the Yongning Gate section alone, including oblique, orthophoto, and manual supplemental captures.
Equipment and Technology
Riebo selected a DJI M300 RTK platform integrated with the Riebo M6 Pros photogrammetry camera.
Key Advantages:
- RTK-level accuracy: centimeter-grade flight precision.
- 3-axis gimbal stabilization: ensures sharp imagery and uniform angles.
- Large 35.7 × 23.8 mm CMOS sensor: captures fine texture and color depth.
- 5 mm-level detail: from ~50 m capture distance.
This configuration ensures balanced efficiency, stability, and detail accuracy for large heritage sites.
Flight Path Planning and Modeling Workflow
Using Way Point Master (WPM) software, an orbit flight plan was executed, which reduced the number of images by 80% compared to traditional five-camera systems — greatly cutting post-processing workload.
Post-flight, data were processed in Mirauge 3D software:
- Aerial triangulation: ≈ 35 minutes
- Model reconstruction: ≈ 3 hours
3D Model Results
The resulting model provides a high-fidelity, photorealistic 3D reconstruction of the Xi’an City Wall.
From wall surfaces to gatehouses and towers, each component exhibits detailed geometry and accurate color mapping, enabling immersive visualization and precise digital management.
Key Results and Insights
- Achieved 4 mm precision at close range; 2 cm GSD for full-wall coverage.
- Reduced total photo count by ~80%, improving efficiency and data quality.
- Demonstrated compatibility with heritage-protection protocols (non-invasive methods).
- Showcased scalability of Riebo’s photogrammetry solution for urban heritage, architectural modeling, and smart city 3D projects.
About Riebo
Our journey began in 2012 when our founding team embarked on this exciting venture. Since then, we have been serving a global customer base, forging robust partnerships with organizations. Our continuous efforts have enabled us to expand our footprint steadily in the aerial surveying and UAV industries, and we remain dedicated to driving the evolution of these fields.
